Observation of pulsed gamma-rays above 25 GeV from the Crab Pulsar with MAGIC
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2008
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Amer Assoc Advancement Science
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Abstract
One fundamental question about pulsars concerns the mechanism of their pulsed electromagnetic emission. Measuring the high- end region of a pulsar's spectrum would shed light on this question. By developing a new electronic trigger, we lowered the threshold of the Major Atmospheric gamma-ray Imaging Cherenkov (MAGIC) telescope to 25 giga-electron volts. In this configuration, we detected pulsed gamma-rays from the Crab pulsar that were greater than 25 giga-electron volts, revealing a relatively high cutoff energy in the phase- averaged spectrum. This indicates that the emission occurs far out in the magnetosphere, hence excluding the polar- cap scenario as a possible explanation of our measurement. The high cutoff energy also challenges the slot- gap scenario.
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© Science. We thank the electronics division at the Max-Planck-Insitut, Munich, for their work in developing and producing the analog sum trigger system, especially O. Reimann, R. Maier, S. Tran, and T. Dettlaff. We also thank L. Stodolsky for comments. We acknowledge the Instituto de Astrofisica for providing all infrastructure on the Roque de los Muchachos in La Palma. The support of the German Bundesministerium fur Bildung, Wissenschaft, Forschung und Technologie and Max-Planck-Gesellschaft, the Italian INFN and INAF, the Swiss Schweizerische Nationalfonds, and Spanish Ministerio de Ciencia e Innovacion is acknowledged. This work was also supported by ETH research grant TH 34/043, by the Polish Ministertwo Nauki i Szkolnictwa Wyzszego grant N N203 390834, and by the Young Investigators Program of the Helmholtz Gemeinschaft.